bacillus

A heat-loving species of bacillus, Bacillus infernus,
collected from deep (20–2800 meters) underground. Photo: U.S.
Dept. of Energy

Any of a large genus of Gram-positive
(see Gram's stain), spore-bearing, rod-shaped
bacteria. Bacilli are widely distributed in
soil and air (usually as spores). Most feed on dead organic material and
are responsible for food spoilage.

Note that the shape of the bacteria can be confused with the name of their
genera. A capital "B" indicates the genus "Bacillus" while a small
"b" indicates the shape (bacillus). Bacillus is a large genus with
many endospore-producing species that are ever
present. Some bacteria are not truly elongated, but can be kidney-shaped,
curved (vibrios), or taper at each end (fusiform bacilli). These do not
have the same arrangements as the cocci,
but may be found in pairs (diplobacilli), or chains (streptobacilli). Bacilli
may be single or adhere end to end to form chains. Some produce spores and
some have flagella for locomotion. Certain
species form a picket-fence pattern, which may look like a stack of wood
(Corynebacterium diphtheriae).